The invention pertains to rotational motion sensors utilizing digital counters and set points that may be digitally indicated.
In the electric motor control art installations utilizing electric motors often have need of a monitoring system for sensing the rate of motion of the apparatus being driven by the motor. For instance, in the material handling art, wherein bulk materials are transported by feed screws, conveyor belts, bucket chains or similar conveying apparatus, it is common to use monitoring devices which indicate that the conveyor is overloaded and is operating at a speed below that for which it was designed. Similar requirements to detect the rate of operation of electric motor driven apparatus exists in the air handling arts, assembly lines, machine control art, food processing plants, and the like.
It is known to monitor the operation of electric motor driven apparatus by sensing devices, and it is also known to monitor the characteristics of electric motors under load by sensing the current or voltage consumption. However, known mechanical and electrical motor sensing controls often are not sensitive enough to malfunctioning and speed variations to provide the degree of precise control desired in low tolerance situations, for instance wherein a deviation of two or three revolutions per second is critical. Also, many known rotation monitoring devices do not react with sufficient speed to prevent damage to the motor under instantaneous stall out and overload conditions.
Rotational motion sensors of an electronic nature are available which are capable of reacting to slow-down, overload and motor stalling conditions, and such rotational sensing circuits usually employ switching means in the form of transistors, and capacitors, in conjunction with control signal pulse producing means driven by the element to be sensed wherein a voltage is permitted to build up at a rate proportional to the duration of the control pulse and is discharged intermediate control pulses. Deviations between the time interval of control pulses beyond the predetermined tolerances of the control circuit will produce a voltage energizing an alarm or control signal. Apparatus of this nature is shown in the assignee's U.S. Pat. No. 3,845,375.
However, electronic rotational sensing apparatus presently available, such as disclosed in assignee's prior mentioned patent, cannot readily be adjusted to operate within very close tolerances, nor can such apparatus be preset to produce an alarm or control signal at two set points wherein alarm signals are produced at two values of deviation from the norm.